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Diffstat (limited to 'library/core/src/str/converts.rs')
| -rw-r--r-- | library/core/src/str/converts.rs | 203 |
1 files changed, 203 insertions, 0 deletions
diff --git a/library/core/src/str/converts.rs b/library/core/src/str/converts.rs new file mode 100644 index 000000000..b0c55ca4f --- /dev/null +++ b/library/core/src/str/converts.rs @@ -0,0 +1,203 @@ +//! Ways to create a `str` from bytes slice. + +use crate::mem; + +use super::validations::run_utf8_validation; +use super::Utf8Error; + +/// Converts a slice of bytes to a string slice. +/// +/// A string slice ([`&str`]) is made of bytes ([`u8`]), and a byte slice +/// ([`&[u8]`][byteslice]) is made of bytes, so this function converts between +/// the two. Not all byte slices are valid string slices, however: [`&str`] requires +/// that it is valid UTF-8. `from_utf8()` checks to ensure that the bytes are valid +/// UTF-8, and then does the conversion. +/// +/// [`&str`]: str +/// [byteslice]: slice +/// +/// If you are sure that the byte slice is valid UTF-8, and you don't want to +/// incur the overhead of the validity check, there is an unsafe version of +/// this function, [`from_utf8_unchecked`], which has the same +/// behavior but skips the check. +/// +/// If you need a `String` instead of a `&str`, consider +/// [`String::from_utf8`][string]. +/// +/// [string]: ../../std/string/struct.String.html#method.from_utf8 +/// +/// Because you can stack-allocate a `[u8; N]`, and you can take a +/// [`&[u8]`][byteslice] of it, this function is one way to have a +/// stack-allocated string. There is an example of this in the +/// examples section below. +/// +/// [byteslice]: slice +/// +/// # Errors +/// +/// Returns `Err` if the slice is not UTF-8 with a description as to why the +/// provided slice is not UTF-8. +/// +/// # Examples +/// +/// Basic usage: +/// +/// ``` +/// use std::str; +/// +/// // some bytes, in a vector +/// let sparkle_heart = vec![240, 159, 146, 150]; +/// +/// // We know these bytes are valid, so just use `unwrap()`. +/// let sparkle_heart = str::from_utf8(&sparkle_heart).unwrap(); +/// +/// assert_eq!("💖", sparkle_heart); +/// ``` +/// +/// Incorrect bytes: +/// +/// ``` +/// use std::str; +/// +/// // some invalid bytes, in a vector +/// let sparkle_heart = vec![0, 159, 146, 150]; +/// +/// assert!(str::from_utf8(&sparkle_heart).is_err()); +/// ``` +/// +/// See the docs for [`Utf8Error`] for more details on the kinds of +/// errors that can be returned. +/// +/// A "stack allocated string": +/// +/// ``` +/// use std::str; +/// +/// // some bytes, in a stack-allocated array +/// let sparkle_heart = [240, 159, 146, 150]; +/// +/// // We know these bytes are valid, so just use `unwrap()`. +/// let sparkle_heart = str::from_utf8(&sparkle_heart).unwrap(); +/// +/// assert_eq!("💖", sparkle_heart); +/// ``` +#[stable(feature = "rust1", since = "1.0.0")] +#[rustc_const_stable(feature = "const_str_from_utf8_shared", since = "1.63.0")] +#[rustc_allow_const_fn_unstable(str_internals)] +pub const fn from_utf8(v: &[u8]) -> Result<&str, Utf8Error> { + // FIXME: This should use `?` again, once it's `const` + match run_utf8_validation(v) { + Ok(_) => { + // SAFETY: validation succeeded. + Ok(unsafe { from_utf8_unchecked(v) }) + } + Err(err) => Err(err), + } +} + +/// Converts a mutable slice of bytes to a mutable string slice. +/// +/// # Examples +/// +/// Basic usage: +/// +/// ``` +/// use std::str; +/// +/// // "Hello, Rust!" as a mutable vector +/// let mut hellorust = vec![72, 101, 108, 108, 111, 44, 32, 82, 117, 115, 116, 33]; +/// +/// // As we know these bytes are valid, we can use `unwrap()` +/// let outstr = str::from_utf8_mut(&mut hellorust).unwrap(); +/// +/// assert_eq!("Hello, Rust!", outstr); +/// ``` +/// +/// Incorrect bytes: +/// +/// ``` +/// use std::str; +/// +/// // Some invalid bytes in a mutable vector +/// let mut invalid = vec![128, 223]; +/// +/// assert!(str::from_utf8_mut(&mut invalid).is_err()); +/// ``` +/// See the docs for [`Utf8Error`] for more details on the kinds of +/// errors that can be returned. +#[stable(feature = "str_mut_extras", since = "1.20.0")] +#[rustc_const_unstable(feature = "const_str_from_utf8", issue = "91006")] +pub const fn from_utf8_mut(v: &mut [u8]) -> Result<&mut str, Utf8Error> { + // This should use `?` again, once it's `const` + match run_utf8_validation(v) { + Ok(_) => { + // SAFETY: validation succeeded. + Ok(unsafe { from_utf8_unchecked_mut(v) }) + } + Err(err) => Err(err), + } +} + +/// Converts a slice of bytes to a string slice without checking +/// that the string contains valid UTF-8. +/// +/// See the safe version, [`from_utf8`], for more information. +/// +/// # Safety +/// +/// The bytes passed in must be valid UTF-8. +/// +/// # Examples +/// +/// Basic usage: +/// +/// ``` +/// use std::str; +/// +/// // some bytes, in a vector +/// let sparkle_heart = vec![240, 159, 146, 150]; +/// +/// let sparkle_heart = unsafe { +/// str::from_utf8_unchecked(&sparkle_heart) +/// }; +/// +/// assert_eq!("💖", sparkle_heart); +/// ``` +#[inline] +#[must_use] +#[stable(feature = "rust1", since = "1.0.0")] +#[rustc_const_stable(feature = "const_str_from_utf8_unchecked", since = "1.55.0")] +pub const unsafe fn from_utf8_unchecked(v: &[u8]) -> &str { + // SAFETY: the caller must guarantee that the bytes `v` are valid UTF-8. + // Also relies on `&str` and `&[u8]` having the same layout. + unsafe { mem::transmute(v) } +} + +/// Converts a slice of bytes to a string slice without checking +/// that the string contains valid UTF-8; mutable version. +/// +/// See the immutable version, [`from_utf8_unchecked()`] for more information. +/// +/// # Examples +/// +/// Basic usage: +/// +/// ``` +/// use std::str; +/// +/// let mut heart = vec![240, 159, 146, 150]; +/// let heart = unsafe { str::from_utf8_unchecked_mut(&mut heart) }; +/// +/// assert_eq!("💖", heart); +/// ``` +#[inline] +#[must_use] +#[stable(feature = "str_mut_extras", since = "1.20.0")] +#[rustc_const_unstable(feature = "const_str_from_utf8_unchecked_mut", issue = "91005")] +pub const unsafe fn from_utf8_unchecked_mut(v: &mut [u8]) -> &mut str { + // SAFETY: the caller must guarantee that the bytes `v` + // are valid UTF-8, thus the cast to `*mut str` is safe. + // Also, the pointer dereference is safe because that pointer + // comes from a reference which is guaranteed to be valid for writes. + unsafe { &mut *(v as *mut [u8] as *mut str) } +} |